200 deg C is marginal. In addition to high-temp couplant [I prefer silicone 'vacuum' grease] and preheating both calibration blocks -- IIW and DAC curve standards to closly match the actual weld temp, you will have to 'baby' your transducer and wedge. The wedge will need to be hi-temp material [phenolic or similar], but the transducer can be a standard 'ducer IF you cool the wedge in water every minute or so [without shorting out the 'ducer]. Additionally, the UT operator will be rather slow, due to the danger of severe burns and the difficulty of properly manipulating the 'ducer with heavy gloves on.
Do not take any shortcuts on calibration, including the refracted angle. There is a large change in metal velocity going from 25 to 200 degrees, the attenuation rate changes, etc.
21:05 Jul-01-2009 Michel Couture NDT Inspector, , consultant, Canada, Joined Sep 2006 607
I've read a few of these queries regarding High Temp UT and I find it strange that no one has questionned the possiblility of Cold Cracking? I was told about this when I started doing weld inspection, so I wonder why one would do weld inspection at 200 ÂºC., let alone the possiblility of burning oneself...
21:28 Jul-01-2009 Tom Nelligan Engineering, , Olympus NDT, USA, Joined Nov 1998 377
You should also keep in mind that even when using a high temperature wedge, the refracted beam angle will change as the wedge temperature changes, due to the changes in wedge velocity. As a practical matter, this can be very difficult to reliably track. You may wish to read our application note on high temperature ultrasonic testing for further discussion
I know you are getting very good technical replies. However, I get one basic doubt, which you can also think over and of course, the other NDT experts are also welcome to share their wisdom.
Is it really necessary for the UT to be done at 200 C? From the question I get a feeling that you are talking of a pipeline in a factory used to carry some fluids and or steam / some other gases. Can't there be a shut down in such a case and the UT performed during the shut down when the pipe will be at the ambient temperature?
Also, a hot pipe would normally be insulated to keep the energy losses low. Have you considered the need for removing the insulation before test and reinstalling the insulation after the test? And have the plant operators considered the thermal losses when the insulation is removed for the duration of the test?
RT may be a better option if the pipe welds indeed need to be tested at the high temperature and you could in theory do it without removing the thermal insulation!
Trying to answer such questions will be helpful not only for the NDT inspectors but to the management in general.
You are right practically the line is insulated,and RT would be beneficial,but from a operating(nucleonics/tripping) point of view RT cannot be used in some operating conditions especially in the upstream oil industry,and the planned shutdown may be months away,hence knowing the conditon of the existing welds becoms a priority especially when we have a inservice weld failure,eg which is attributed to weld root corrosion.Knowing the existing condition of the remaining welds becomes a priority so that we could migitate the risk
In this instance i would strip the insulation from the welds and inspect them by UT,though some govt legislations donot allow this from a operator safety point of view,but practically you could.
11:07 Jul-02-2009 Mark Nel , Business Development Manager, IMechE, United Kingdom, Joined Jul 2005 52
There is an old technique for root erosion/corrosion validation using ToFD viewed on an unrectified A-Scan display and using simple purpose-made reference blocks that was or perhaps still still is widely used in the North Sea. This technique is very fast therefore minimising contact time with the hot surface to no more than a minute or two. Perhaps some of our older members with experience of this technique may shed some light as to whether it could be used for Ovidiu's application effectively.
17:03 Jul-02-2009 Luis Ganhao Engineering, Sr. Asset Integrity-Materials & Welding Specialist, USA, Joined Sep 2008 25
Please try with EMAT (elctromaganetic trasnducers UT) I think this technique is one of the more used in this case, there is some companies that perform a lot of inspections at high temp. with EMAT one of them is MATRIX and IRISNDT
EMATs can be used easily to inspect welded seams at high temperature (>200 C). I am not sure what is the thickness range of the pipes. If guided waves are possible EMAT would be a great solution. We have done high temperature applications with EMAT ( 650 C and above) for thickness measurements and probes are presently working in line at plants in USA.
Please refer to www.innerspec.com for further information.
22:08 Jul-06-2009 Abbas Bombaywala NDT Inspector, Free Lance, India, Joined Jul 2007 83
Well high temprature increase too many parameters to be kept in mind for Ultrasonic Testing, Your Cal Block need preheating upto the temprature of material to be inspected, The wedge temprature to be maintained by cooling the wedge after certain time. Change in wedge temprature will give u change in your angle. EMAT Probes is a good option as advised by other NDT Technician,
But i agree with the points of Mr Swamy, Cause u cant be reliable for high temprature inspections as practicaly there are too many difficulties to inspect a weld above 100 degree temprature, more over there is a chance of Operator getting burnt. So better to do a radiography. Other NDT Specialist might have other views, There are too many NDT Companies doing a high temprature UT & Corrosion Mapping including our company "SGS"